1. Field of the Invention
The present invention relates to a USB compound device, a USB system including the present USB compound device, and a related method; and more particularly, to a USB compound device utilizing a plurality of USB dummy devices for initializing a plurality of USB devices of the USB compound device, and also to a USB system including the said USB compound device and a related method.
2. Description of the Prior Art
Universal Serial Bus (USB) is a very common computer interface specification. Usually a personal computer (PC) provides at least one standard USB port. Any peripheral device that implements the USB standard can connect to a PC equipped with a USB port and transmit/receive data through the USB port. With the ease of use provided by plug-and-play, and the high transmission speed, devices using the USB standard interface are now in the mainstream. USB flash memory cards for digital cameras and USB hard disks are just two examples. Usually, USB devices can only be initialized correctly by a USB system when connecting to a downstream port of a USB hub on a one-to-one basis. There are some USB compound devices on the market. These USB compound devices comprise at least two USB devices within them. For example, a USB input device may comprise a keyboard and a trackball. A conventional USB compound device must includes a USB hub such that the plurality of USB devices of the USB compound device can operate correctly.
Please refer to FIG. 1. FIG. 1 is a block diagram of a prior art USB system 100 including a USB compound device 120. The USB system 100 includes a USB host 110, a USB hub 160, and a conventional USB compound device 120. The USB hub 160 comprises an upstream port 162, a first downstream port 1641 and a second downstream port 1642. The USB compound device 120 comprises a USB hub 130 and two USB devices 140 and 150. The function and structure of the USB hub 130 is the same as a common USB hub. The embedded USB hub 130 includes an upstream port 132 and a plurality of downstream ports. In the example illustrated in FIG. 1, there are a first downstream port 1341 and a second downstream port 1342 in the embedded USB hub 130. The two downstream ports 1341 and 1342 of the USB hub 130 connect to the two upstream ports 142 and 152 of the USB devices 140 and 150 respectively within the USB compound device 120, and the whole USB compound device 120 connects to the USB system 100 by connecting the downstream port 1641 of the USB hub 160 with its upstream port 132. In the USB system 100 illustrated in FIG. 1, although the USB host 110 can directly connect to the embedded USB hub 130 of the USB compound device 120 instead of connecting the individual USB hub 160 first, common USB hosts such as PCs are all equipped with a USB root hub. Therefore, the USB system 100 illustrated in FIG. 1 still comprises a USB hub 160.
Please refer to FIG. 2. FIG. 2 is a flowchart of a conventional USB host initializing a USB compound device. The prior art USB system 100 and its components illustrated in FIG. 1 are utilized to demonstrate the flow of initialization in FIG. 2.
Step 200: Start;
Step 202: USB host 110 detects an unset device 160;
Step 204: USB host 110 initializes USB hub 160 and gets information;
Step 206: USB hub 160 detects an unset device 130 connected to the first downstream port 1641;
Step 208: USB host 110 queries USB hub 160 and gets downstream port status-change information;
Step 210: USB host 110 initializes USB hub 130 and gets information;
Step 212: USB hub 130 detects an unset device 140 connected to the first downstream port 1341;
Step 214: USB host 110 queries USB hub 130 and gets downstream port status-change information;
Step 216: USB host 110 initializes USB device 140 and gets information about USB device 140; USB host 110 assigns a unique address to USB device 140;
Sep 218: USB hub 130 detects an unset device 150 connected to the second downstream port 1342;
Step 220: USB host 110 queries USB hub 130 and gets downstream port status-change information;
Step 222: USB host 110 initializes USB device 150 and gets information; USB host 110 assigns a unique address to USB device 150;
Step 224: End.
It can be seen in the flowchart illustrated in FIG. 2 that the conventional USB compound device must comprise an embedded USB hub for each of the plurality of USB devices of the USB compound device to be initialized and assigned an address by the USB host correctly, and for the USB host to control the plurality of USB devices of the USB compound device properly. However, the requirement of an embedded USB hub raises the complexity of the structure of the USB compound device, and the cost of the conventional USB compound device increases in consequence.